Die rolls in Magic comes from cards that instruct you to roll dice and then reward particular results. Although twenty-sided dice are especially common, Magic cards can call for several different types of dice depending on the effect.
Ancient Copper Dragon converts a d20 roll into a potentially absurd pile of Treasure, while Mr. House, President and CEO rewards high rolls with additional artifact tokens. Cards such as Krark's Other Thumb can make the whole enterprise even stranger where legal.